Merge pull request #1423 from hansmaulwurf23/issue_1378

cloning old data before updating to fix #1378

lib/DataSet.js

@@ -243,10 +243,11 @@ DataSet.prototype.update = function (data, senderId) {
   var addOrUpdate = function (item) {
     var id = item[fieldId];
     if (me._data[id]) {
+      var oldData = util.extend({}, me._data[id]);
       // update item
       id = me._updateItem(item);
       updatedIds.push(id);
-      updatedData.push(item);
+      updatedData.push(oldData);
     }
     else {
       // add new item
@@ -273,7 +274,15 @@ DataSet.prototype.update = function (data, senderId) {
     this._trigger('add', {items: addedIds}, senderId);
   }
   if (updatedIds.length) {
-    this._trigger('update', {items: updatedIds, data: updatedData}, senderId);
+	var props = { items: updatedIds, oldData: updatedData };
+	// TODO: remove deprecated property 'data' some day
+	Object.defineProperty(props, 'data', {
+	  'get': (function() {
+	    console.warn('Property data is deprecated. Use DataSet.get(ids) to retrieve the new data, use the oldData property on this object to get the old data');
+	    return this.get(updatedIds);
+	  }).bind(this)
+	});
+    this._trigger('update', props, senderId);
   }
 
   return addedIds.concat(updatedIds);
@@ -513,7 +522,7 @@ DataSet.prototype.forEach = function (callback, options) {
   var filter = options && options.filter,
       type = options && options.type || this._options.type,
       data = this._data,
-      itemIds = Object.key(data),
+      itemIds = Object.keys(data),
       i,
       len,
       item,